BIOL 304 Lecture Notes - Lecture 25: Experimental Evolution, Selection Coefficient, Operon
Document Summary
The e coli inoculation experiment (by competitive assay) Ancestor and evolved lines are grown together, at different time, cultured on dish and selection coefficient is counted through colony numbers. Fitness increases rapidly at first, then slows down over time. Beneficial mutation of large effects are being substituted first. At constant environment and well adapted, purifying selection prevents changes. When a mutation is fixed, it eliminates other variations, cause a pause in fitness increase. Resulted because the waiting time of substitution is longer than passage time. Due to stochastic of mutation (different mutation and fixation schedule) Different degree of loss of function and modification of d-ribose across lines. General targets of modification (e. g. ribose operon) are modified more often. Beneficial mutations often restricted to a few genes and specific sites within. Outcome of adaptation is predictable (limited outcome of metabolism, e. g. lactose to galactose and glucose) Adaptive walks: different genetic route to obtain the same adaptive phenotype (under same conditions?)
